ext4: serialize dio nonlocked reads with defrag workers

Inode's block defrag and ext4_change_inode_journal_flag() may
affect nonlocked DIO reads result, so proper synchronization
required.

- Add missed inode_dio_wait() calls where appropriate
- Check inode state under extra i_dio_count reference.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

4 files changed, 44 insertions, 0 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index edb049579420..1be2b4472a83 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1358,6 +1358,8 @@ enum {
         EXT4_STATE_DIO_UNWRITTEN,       /* need convert on dio done*/
         EXT4_STATE_NEWENTRY,            /* File just added to dir */
         EXT4_STATE_DELALLOC_RESERVED,   /* blks already reserved for delalloc */
+        EXT4_STATE_DIOREAD_LOCK,        /* Disable support for dio read
+                                           nolocking */
 };
 
 #define EXT4_INODE_BIT_FNS(name, field, offset)                         \
@@ -2469,6 +2471,21 @@ static inline void set_bitmap_uptodate(struct buffer_head *bh)
         set_bit(BH_BITMAP_UPTODATE, &(bh)->b_state);
 }
 
+/*
+ * Disable DIO read nolock optimization, so new dioreaders will be forced
+ * to grab i_mutex
+ */
+static inline void ext4_inode_block_unlocked_dio(struct inode *inode)
+{
+        ext4_set_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
+        smp_mb();
+}
+static inline void ext4_inode_resume_unlocked_dio(struct inode *inode)
+{
+        smp_mb();
+        ext4_clear_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
+}
+
 #define in_range(b, first, len) ((b) >= (first) && (b) <= (first) + (len) - 1)
 
 /* For ioend & aio unwritten conversion wait queues */
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 61f13e57975e..8d849dae8428 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -810,11 +810,25 @@ retry:
                 if (unlikely(!list_empty(&ei->i_completed_io_list)))
                         ext4_flush_completed_IO(inode);
 
+                /*
+                 * Nolock dioread optimization may be dynamically disabled
+                 * via ext4_inode_block_unlocked_dio(). Check inode's state
+                 * while holding extra i_dio_count ref.
+                 */
+                atomic_inc(&inode->i_dio_count);
+                smp_mb();
+                if (unlikely(ext4_test_inode_state(inode,
+                                                    EXT4_STATE_DIOREAD_LOCK))) {
+                        inode_dio_done(inode);
+                        goto locked;
+                }
                 ret = __blockdev_direct_IO(rw, iocb, inode,
                                  inode->i_sb->s_bdev, iov,
                                  offset, nr_segs,
                                  ext4_get_block, NULL, NULL, 0);
+                inode_dio_done(inode);
         } else {
+locked:
                 ret = blockdev_direct_IO(rw, iocb, inode, iov,
                                  offset, nr_segs, ext4_get_block);
 
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 09d0488e9a15..bdd399bc2abf 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4720,6 +4720,10 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
                         return err;
         }
 
+        /* Wait for all existing dio workers */
+        ext4_inode_block_unlocked_dio(inode);
+        inode_dio_wait(inode);
+
         jbd2_journal_lock_updates(journal);
 
         /*
@@ -4739,6 +4743,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
         ext4_set_aops(inode);
 
         jbd2_journal_unlock_updates(journal);
+        ext4_inode_resume_unlocked_dio(inode);
 
         /* Finally we can mark the inode as dirty. */
 
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 8076b96b5299..292daeeed455 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -1323,6 +1323,12 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
         /* Protect orig and donor inodes against a truncate */
         mext_inode_double_lock(orig_inode, donor_inode);
 
+        /* Wait for all existing dio workers */
+        ext4_inode_block_unlocked_dio(orig_inode);
+        ext4_inode_block_unlocked_dio(donor_inode);
+        inode_dio_wait(orig_inode);
+        inode_dio_wait(donor_inode);
+
         /* Protect extent tree against block allocations via delalloc */
         double_down_write_data_sem(orig_inode, donor_inode);
         /* Check the filesystem environment whether move_extent can be done */
@@ -1521,6 +1527,8 @@ out:
                 kfree(holecheck_path);
         }
         double_up_write_data_sem(orig_inode, donor_inode);
+        ext4_inode_resume_unlocked_dio(orig_inode);
+        ext4_inode_resume_unlocked_dio(donor_inode);
         mext_inode_double_unlock(orig_inode, donor_inode);
 
         return ret;